As the demand for heat resistance of materials to be used in automobile engines increases, gaskets made of silicone rubber have been broadly used for sealing of an engine and its surroundings. In particular, formed-in-place gaskets (hereinafter referred to as "FIPG") made from a curable liquid silicone rubber have been replacing conventional cut-to-size gaskets for ease of inventory control of gaskets, ease of process control in production of engines, and high reliability of sealing performance. The advantages of the FIPG system in workability, heat resistance, and the like are now highly appreciated.
Since the engine parts to be sealed are often contaminated with organic oily substances such as hydrocarbon oils, animal or vegetable oils, and synthetic oils as in the case that a rust preventing oil is applied or that the parts are dipped in an engine oil for smooth assembly, the oily contaminants must be wiped off the surface with a cloth, etc., before FIPG sealing. However, since the organic oily substances, such as hydrocarbon oils, are not completely removed, the parts cannot be sealed completely. For example, should an oil pan with its surface contaminated be sealed by an FIPG system, cases are sometimes met with in which such troubles as leakage of an engine oil occurs in use. Further, while an FIPG sealing compound is automatically coated by means of a robot, the above-described wiping operation with a cloth is manually conducted, which has been a bar to automation of a series of operations.
In order to solve these problems, WO 88/05798 (unexamined published international patent application) discloses an adhesive comprising a room temperature-curable organopolysiloxane composition and an oxime(alkoxy)silylalkylurea compound as a fixing agent. Further, JP-A-5-98160 (unexamined published Japanese patent application) discloses an adhesive composition for adhesion to an oil-contaminated surface which comprises the same condensation reaction type organopolysiloxane composition as used in WO 88/500178 and an oil-absorbing carbon powder. However, these compositions still fail to achieve adhesion to an oil-contaminated surface to a satisfactory degree.
Besides the above-described condensation reaction type compositions, addition reaction type organopolysiloxane compositions have been proposed which cure in a short time on heating through addition reaction between an alkenyl group bonded to the silicon atom and an Si--H bond and exhibit excellent deep cure. The organopolysiloxane composition used here generally shows no adhesion by itself but is made into an addition reaction type organopolysiloxane composition having adhesiveness to various substrates by incorporation of an organic amine compound having a vinyl group, a methacryloyl group, an ester linkage, an alkoxy group, in the molecule thereof. The adhesive composition of this type has been widely used as an FIPG compound in places where heat curing is permitted or as an FIPG compound which is used in such a manner that the compound is applied to one element and, after curing, another element is fitted thereto, followed by compression. However, none of the known adhesive addition reaction type organopolysiloxane compositions exhibit excellent adhesion to an oil-contaminated surface.